Ash fusing system, method of operating the system, and gasification fusing system for waste

ABSTRACT

An ash melting system of the present invention includes a slagging combustion furnace ( 10 ) for melting ash into molten slag; and a slag separating apparatus ( 50 ) for bringing the molten slag ( 121 ) discharged from the slagging combustion furnace into contact with slag cooling water ( 152 ) to produce water-quenched slag ( 122 ), and separating the water-quenched slag from the slag cooling water. The ash melting system further includes a gas blowing means for blowing air or inert gas ( 132 ) between a slag discharge port ( 14 ) of the slagging combustion furnace and the surface of the slag cooling water.

TECHNICAL FIELD

[0001] The present invention relates to a melting system for bringingthe molten slag discharged from an ash melting furnace into contact withwater to produce water-quenched slag and a method of operating suchmelting system, and a melting system attached to a gasification andslagging combustion system for combusting various wastes includingmunicipal wastes, refuse-derived fuel (RDF), plastic wastes, waste FRP,biomass wastes, automobile wastes, waste oil, and the like.

BACKGROUND ART

[0002] It has been desired that wastes including municipal wastes,refuse-derived fuel (RDF), plastic wastes, waste FRP, biomass wastes,automobile wastes, waste oil, and the like are safely combusted toreduce the volume of the wastes, and the combustion heat of the wastesis effectively utilized. Because incineration ash usually containsharmful heavy metals, in order to reclaim the incineration ash, it isnecessary to take some measures for stabilizing heavy metal components.Further, there has been a request for downsizing a waste treatmentfacility as a whole. In order to realize the above subjects, agasification and slagging combustion system which can recover variousmetals and harmless slag capable of being effectively utilized, andrecover energy in the form of heat, electric power or the like has beenput to practical use. The gasification and slagging combustion system isnot ordinary incineration, but is capable of performing material andthermal recycling.

[0003] In the gasification and slagging combustion system, wastes arepyrolyzed and gasified at a temperature of 450 to 750° C. to generate agas, tar, char (solid carbon containing ash), and the like in thegasification furnace, and the generated gas and tar are introduced intothe slagging combustion furnace together with particulate char andcombusted by a secondary air at a high temperature under a low air ratioof about 1.3 to about 1.5 to increase a combustion temperature of amelting point of ash or higher (for example, 1300° C. to 1450° C.) inthe slagging combustion furnace. In this high-temperature condition,molten ash is collected on a furnace wall surface and falls along thefurnace wall surface, thus forming a flow of molten slag. This moltenslag is contacted with cooling water to form water-quenched slag.

[0004] An ash melting system does not have a gasification furnace. Inthe ash melting system, ash is supplied directly to a melting furnace toproduce molten slag. The process in which molten slag is converted intowater-quenched slag is substantially same as the above gasification andslagging combustion system. Therefore, details of the ash melting systemwill not be described here.

[0005] Next, a combination of a gasification apparatus comprising afluidized-bed gasification furnace and a slagging combustion furnacecomprising a swirling-type slagging combustion furnace will be describedbelow. FIG. 1 shows a conventional melting system having a swirling-typeslagging combustion furnace and a water quenching trough, and a slagseparating apparatus for separating molten slag.

[0006] In FIG. 1, reference numeral 10 represents a swirling slaggingcombustion furnace (swirling-type slagging combustion furnace),reference numeral 30 represents a water quenching trough, and referencenumeral 50 represents a slag separating apparatus. The swirling-typeslagging combustion furnace 10 comprises a primary combustion chamber11, a secondary combustion chamber 12, and a tertiary combustion chamber13. A produced gas (combustible gas) 111 containing char and tar whichhas been generated by pyrolysis and gasification in a gasificationfurnace (not shown) is introduced into the upper part of the primarycombustion chamber 11 tangentially to an inner wall surface of theprimary combustion chamber 11. Then, the gas 111 is mixed with a gas forcombustion (usually, preheated air) 115 introduced into the primarycombustion chamber 11, and is combusted and flows into the secondarycombustion chamber 12 where the gas is combusted at a high temperatureof about 1300 to about 1450° C. Then, the gas flows into the tertiarycombustion chamber 13 and is completely combusted, and resultantcombustion exhaust gas 113 is then supplied to a waste heat boiler (notshown). In FIG. 1, reference numerals 15 and 16 represent a burner forstartup and auxiliary heat supply of the slagging combustion furnace,respectively.

[0007] The generated gas 111 containing char and tar which has beenintroduced into the upper part of the primary combustion chamber 11forms a swirling flow, and moves to the secondary combustion chamber 12while it is combusted at a high temperature in the swirling flow. Undercentrifugal forces by the swirling flow, ash contained in the char ischanged to slag mists and collected on the furnace wall surface. Theslag mists attached to the furnace wall surface form a layer of moltenslag 121, and the molten slag 121 flows down the bottom of the secondarycombustion chamber 12, then falls from a slag discharge port 14 onto thewater quenching trough 30. Water for cooling molten slag (hereinafterreferred to as slag cooling water 152) flows on the water quenchingtrough 30 at all times. The molten slag 121 which has fallen from theslag discharge port 14 is dropped into the slag cooling water 152 andquenched to form water-quenched slag 122. The water-quenched slag 122flows together with the slag cooling water 152 into a water tank 51 ofthe slag separating apparatus 50. The water tank 51 has a slag settlingfunction. The settled water-quenched slag is scraped and removed byscrapers 53 attached to a separating conveyor 52, and is carriedupwardly and separated from the slag cooling water. The water-quenchedslag 122 is then discharged from the separating conveyor 52 through aslag discharge opening 54 to the outside of the slag separatingapparatus 50. The slag cooling water 152 in the water tank 51 isdelivered by a pump 41 from the water tank 51 onto the water quenchingtrough 30 through a pipe-line 151 and a nozzle 32. The slag coolingwater 152 is circulated and reused.

[0008] The slag discharge port 14 serves to discharge molten slag 121from the swirling-type slagging combustion furnace 10. However, becausethe swirling-type slagging combustion furnace 10 is filled with theexhaust gas 112, the molten slag 121 accompanies the exhaust gas 112which is going to be contacted with the slag cooling water 152unavoidably. Since the exhaust gas 112 contains many componentsincluding harmful substances, the exhaust gas 112 tends to contaminatethe slag cooling water 152 and deteriorates the quality of the slagcooling water 152 by being contacted with the slag cooling water 152. Asa result, the recovered water-quenched slag 122 is contaminated by theslag cooling water 152.

[0009] When the high-temperature molten slag 121 is contacted with theslag cooling water 152, a part of the slag cooling water 152 isevaporated, and the generated steam goes up to cool the slag dischargeport 14. Consequently, the molten slag 121 is liable to be solidified onthe inner surface of the slag discharge port 14 and the portion aroundthe slag discharge port 14, and in extreme cases, the slag dischargeport 14 is clogged with the solidified slag.

DISCLOSURE OF INVENTION

[0010] The present invention has been made in view of the abovedrawbacks. It is therefore an object of the present invention to providean ash melting system, a method of operating a melting furnaceapparatus, and a gasification and slagging combustion system, forproducing water-quenched slag by bringing molten slag discharged from aslagging combustion furnace into contact with slag cooling water, whichcan prevent exhaust gas discharged together with the molten slag fromthe slagging combustion furnace (melting furnace) from contacting theslag cooling water, prevent a slag discharge port and a portion aroundthe slag discharge port from being cooled by steam evaporated from theslag cooling water, and prevent the water-quenched slag from being madeworse in quality due to a deterioration in the quality of the slagcooling water (if the slag cooling water is contaminated, thecontaminated slag cooling water is adhered to the surface of the slaggranules to cause a deterioration in the quality of water-quenchedslag).

[0011] Another object of the present invention is to provide a cleaningsystem for removing harmful contaminants such as heavy metals which mayhave been adhered to the surfaces of water-quenched slag granules, evenif exhaust gas discharged together with molten slag from a slaggingcombustion furnace is not fully prevented from contacting slag coolingwater.

[0012] In order to achieve the above objects, according to the presentinvention, there is provided an ash melting system comprising: aslagging combustion furnace for melting ash into molten slag anddischarging the molten slag from a slag discharge port; a slagseparating apparatus for bringing the molten slag into contact with slagcooling water to produce water-quenched slag, and separating thewater-quenched slag from the slag cooling water; and a gas blowing meansfor blowing air or inert gas between the slag discharge port of theslagging combustion furnace and the surface of the slag cooling water.

[0013] As described above, the gas blowing means is provided to blow airor inert gas between the slag discharge port of the slagging combustionfurnace and the surface of the slag cooling water, thus preventinggas-liquid contact of exhaust gas and the slag cooling water. Therefore,the slag cooling water is prevented from being deteriorated in quality.

[0014] According to one aspect of the present invention, the systemfurther comprises a gas mixture line for drawing a gas mixture ofexhaust gas discharged from the slag discharge port of the slaggingcombustion furnace and the air or inert gas blown from the gas blowingmeans and supplying the gas mixture into the slagging combustionfurnace.

[0015] As mentioned above, the gas mixture line is provided to draw agas mixture from the slag discharge port and to supply the gas mixtureinto the slagging combustion furnace. The gas mixture line draws the airor inert gas blown between the slag discharge port and the surface ofthe slag cooling water and also steam evaporated from the slag coolingwater, thus preventing the slag discharge port and its vicinity frombeing cooled. The line also draws the exhaust gas having a hightemperature through the slag discharge port from the slagging combustionfurnace, thus keeping the slag discharge port and the portion around theslag discharge port at a high temperature. If the gas that has beenblown in is the air, because the air is supplied through the gas mixtureline into the slagging combustion furnace, the air can be utilized ascombustion air.

[0016] According to one aspect of the present invention, the systemfurther comprises a flow control means provided in the gas mixture linefor controlling the flow rate of the gas mixture drawn by the gasmixture line.

[0017] As mentioned above, the flow control means can regulate the flowrate of the gas mixture drawn from the slag discharge portion.

[0018] According to one aspect of the present invention, the systemfurther comprises a temperature sensor provided in the gas mixture linefor measuring the temperature of the gas mixture in the gas mixtureline; wherein the flow control means is operated on a basis of an outputof the temperature sensor to control the flow rate of the gas mixturedrawn by the gas mixture line to equalize the temperature of the gasmixture line with a set temperature.

[0019] The set temperature has a lower limit which is higher than thedew point of hydrogen chloride contained in the exhaust gas forpreventing low-temperature corrosion. The set temperature has an upperlimit which is determined depending on the allowable temperatures ofpipes and a fan. Usually, the set temperature is set in a temperaturerange in which inexpensive carbon steel can be used. Specifically, thegas mixture line is preferably controlled in the range of 110 to 350° C.

[0020] As described above, the temperature sensor is provided to measurea temperature of the gas mixture, and the flow control means controlsthe rate of the gas mixture drawn by the gas mixture line, thus keepingthe temperature of the gas mixture line at the set temperature on abasis of the output from the temperature sensor. If the set temperatureis set to a value equal to or lower than the allowable temperature ofthe fan provided in the gas mixture line, then the temperature of thegas mixture line can be kept to be equal to or lower than the allowabletemperature of the fan, low-temperature corrosion of ducts of the gasmixture line and the fan is prevented.

[0021] According to an ash melting system of the present invention, slagdischarged from a slagging combustion furnace is supplied together withslag cooling water to a water tank having a settling and separatingfunction, the slag which has been settled and separated is removed froma bottom of the water tank and conveyed above the surface of the slagcooling water in the water tank, and then the slag is cleaned bycleaning water supplied from the cleaning water supply system.

[0022] With the above arrangement, harmful impurities such as heavymetals attached to the surfaces of the water-quenched slag can beremoved from the water-quenched slag, and hence the water-quenched slagof good quality can be recovered.

[0023] Furthermore, even if the exhaust gas discharged together with themolten slag from the slagging combustion furnace is not completelyprevented from contacting the slag cooling water, the same cleaningeffect can be obtained.

[0024] According to one aspect of the present invention, there isprovided a method of operating an ash melting system for melting ashinto molten slag and discharging the molten slag from a slag dischargeport in a slagging combustion furnace, and producing water-quenched slagby bringing the molten slag into contact with slag cooling water, themethod comprising: blowing air or inert gas between the slag dischargeport of the slagging combustion furnace and the surface of the slagcooling water to prevent gas-liquid contact of exhaust gas dischargedfrom the slagging combustion furnace and the slag cooling water.

[0025] As described above, when the air or inert gas is blown betweenthe slag discharge port of the slagging combustion furnace and thesurface of the slag cooling water, the exhaust gas is prevented fromcontacting the slag cooling water, and hence the slag cooling water isprevented from being lowered in quality. The water-quenched slag is thusprevented from being lowered in quality due to a deterioration in thequality of the slag cooling water.

[0026] According to another aspect of the present invention, there isprovided a method of operating an ash melting system for melting ash,comprising: producing water-quenched slag from molten slag dischargedfrom a slagging combustion furnace by bringing the molten slag intocontact with slag cooling water; supplying the water-quenched slagtogether with slag cooling water to a water tank having a settling andseparating function; removing the settled water-quenched slag from abottom of the water tank to separate the water-quenched slag from theslag cooling water; and supplying cleaning water supplied from acleaning water supply system onto the water-quenched slag to clean thewater-quenched slag after the water-quenched slag is removed from thebottom of the water tank and is conveyed above the surface of the slagcooling water in the water tank.

[0027] As described above, after the water-quenched slag is removed fromthe bottom of the water tank, the water-quenched slag is cleaned by thecleaning water supplied from the cleaning water supply system.Consequently, harmful impurities such as heavy metals attached to thesurfaces of the water-quenched slag can be removed from thewater-quenched slag, and hence the water-quenched slag of good qualitycan be recovered.

[0028] According to one aspect of the present invention, there isprovided a gasification and slagging combustion system of wastescomprising: a gasification furnace for gasifying wastes to generategasification products; a slagging combustion furnace for combusting thegasification products to produce molten slag; a water-quenched slagproducing mechanism for producing water-quenched slag by bringing slagdischarged from the slagging combustion furnace into contact with slagcooling water; and a gas blowing means for blowing air or inert gasbetween a slag discharge port of the slagging combustion furnace and thesurface of the slag cooling water.

[0029] As described above, the gas blowing means is provided to blow theair or inert gas between the slag discharge port of the slaggingcombustion furnace and the surface of the slag cooling water, thuspreventing exhaust gas discharged from the slagging combustion furnacethrough the slag discharge port from contacting the slag cooling water.Therefore, the gasification and slagging combustion system can beconstructed such that the slag cooling water is prevented from beinglowered in quality.

[0030] According to another aspect of the present invention, there isprovided a gasification and slagging combustion system of wastescomprising: a gasification furnace for gasifying wastes to generategasification products; and a slagging combustion furnace for combustingthe gasification products to produce molten slag, wherein water-quenchedslag is produced by bringing the molten slag discharged from theslagging combustion furnace into contact with slag cooling water, thewater-quenched slag is supplied together with the slag cooling water toa water tank having a settling and separating function, and the settledwater-quenched slag is removed from a bottom of the water tank toseparate the water-quenched slag from the slag cooling water; whereincleaning water supplied from a cleaning water supply system is suppliedonto the slag to clean the slag after the slag is removed from thebottom of the water tank and is conveyed above the surface of the slagcooling water.

[0031] According to the gasification and slagging combustion system ofwastes, the water-quenched slag is removed from the bottom of the watertank, and then the cleaning water supplied from the cleaning watersupply system is supplied to the water-quenched slag to remove harmfulimpurities such as heavy metals attached to the surfaces of thewater-quenched slag, and hence the water-quenched slag of good qualitycan be recovered.

BRIEF DESCRIPTION OF DRAWINGS

[0032]FIG. 1 is a schematic view of a conventional melting furnaceapparatus having a swirling-type slagging combustion furnace (meltingfurnace), a water quenching trough, and a slag separating conveyorapparatus;

[0033]FIG. 2 is a schematic view of a melting system having aswirling-type slagging combustion furnace, a water quenching trough, anda slag separating conveyor apparatus according to the present invention;

[0034]FIG. 3 is a schematic view showing a slag discharge port and aportion around the slag discharge port in a slagging combustion furnaceaccording to the present invention;

[0035]FIG. 4 is a schematic view of a melting system having aswirling-type slagging combustion furnace, a water quenching trough, anda slag separating conveyor apparatus according to the present invention;

[0036]FIG. 5 is a schematic view of a melting system having aswirling-type slagging combustion furnace and a slag separating conveyorapparatus according to the present invention; and

[0037]FIG. 6 is a schematic view showing a slag discharge port and aportion around the slag discharge port in a slagging combustion furnaceaccording to the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

[0038] Next, embodiments of the present invention will be described withreference to the drawings. FIG. 2 is a schematic view showing agasification and slagging combustion system having a swirling-typeslagging combustion furnace, a water quenching trough, and a slagseparating apparatus according to the present invention. Thegasification and slagging combustion system has a swirling-type slaggingcombustion furnace 10, a water quenching trough 30, and a slagseparating apparatus 50. The swirling-type slagging combustion furnace10 comprises a primary combustion chamber 11, a secondary combustionchamber 12, and a tertiary combustion chamber 13. A produced gas 111produced by pyrolysis of wastes and containing char and tar isintroduced into the upper part of the primary combustion chamber 11, ismixed with a gas 115 for combustion, and moves into the secondarycombustion chamber 12 while it is combusted. In the secondary combustionchamber 12, the gas is combusted at a high temperature of 1300 to 1450°C. Then, the gas passes through the tertiary combustion chamber 13 andbecomes exhaust gas 113, and the exhaust gas 113 is then discharged to awaste heat boiler (not shown).

[0039] The produced gas 111 (combustible gas containing unburned carbonand ash) produced by pyrolysis of wastes and containing char and tar isintroduced into the upper part of the primary combustion chamber 11 in adirection tangential to an axis of the primary combustion chamber 11,thereby forming a swirling flow in the primary combustion chamber 11.The swirling flow causes the ash to be collected on the wall surface ofthe primary combustion chamber 11. The collected ash is melted at a hightemperature to form molten slag 121, and the molten slag 121 falls froma slag discharge port 14 through a slag discharge chute 21 into thewater quenching trough 30. The primary and secondary combustion chambers11 and 12 have blowing ports directed to introduce a gas for combustioninto the primary and secondary combustion chambers 11 and 12 in adirection tangential to axes of the primary and secondary combustionchambers 11 and 12. The molten slag 121 which has fallen into the waterquenching trough 30 is brought into contact with slag cooling water 152in the water quenching trough 30 to form water-quenched slag 122. Theformed water-quenched slag 122 is delivered into the slag separatingapparatus 50. In the slag separating apparatus 50, the water-quenchedslag 122 is scraped by scrapers 53 of a separating conveyor 52 and isremoved.

[0040] The gasification and slagging combustion system also has a gasblowing line 131 for blowing air (purge air) or inert gas (purge inertgas) at a discharge end of the water quenching trough 30. The gasblowing line 131 blows the air or inert gas 132 to the lower end of theflow of the slag cooling water 152 (the lower end of theslag-granulating water surface). The introduced air or inert gas 132flows along the slag-cooling water surface into a region between theslag discharge port 14 of the swirling-type slagging combustion furnace10 and the slag-cooling water surface. The air or inert gas 132 thusintroduced is effective to prevent the exhaust gas 112 flowing inthrough the slag discharge port 14 from contacting the slag coolingwater 152.

[0041] In this manner, by preventing gas-liquid contact of the slagcooling water 152 and the exhaust gas 112, the slag cooling water 152 isprevented from being lowered in quality.

[0042] Because the slag cooling water 152 is prevented from beinglowered in quality, the water-quenched slag 122 is also prevented frombeing lowered in quality, i.e., from being lowered in quality bycontaminants of the contaminated slag cooling water which wouldotherwise be attached to the surfaces of the water-quenched slag.

[0043] The air or inert gas 132 blown toward the lower end of theslag-granulating water surface of the water quenching trough 30 iseffective to purge the exhaust gas 112. A plurality of blowing ports maybe provided in the water quenching trough 30 for effectively purging theexhaust gas 112 or preventing the air or inert gas 132 from forminglocalized flows.

[0044] In the gasification and slagging combustion system, thewater-quenched slag 122 produced in the water quenching trough 30 isintroduced into a water tank 51 of the slag separating apparatus 50. Thewater tank 51 has a slag settling capability. The settled water-quenchedslag is scraped by the scrapers 53 and removed from the bottom of thewater tank 51, and separated from the slag cooling water. After theseparated water-quenched slag is scraped and removed from the bottom ofthe water tank and conveyed above the water surface, the water-quenchedslag is cleaned by cleaning water which is supplied from a cleaningwater line 161 and sprayed by a spraying nozzle 55. Thereafter, thewater-quenched slag 122 is conveyed by the separating conveyor 52, anddischarged from a slag discharge opening 54.

[0045] In this manner, after the water-quenched slag is conveyed out ofthe bottom of the water tank 51, the water-quenched slag is cleaned bythe sprayed cleaning water supplied from the cleaning water supplysystem. Consequently, harmful impurities such as heavy metals attachedto the surfaces of the water-quenched slag can be removed from thewater-quenched slag, and hence the water-quenched slag 122 of goodquality can be recovered.

[0046] By spraying the cleaning water from the cleaning water line 161,the cleaning water infiltrates frictional components (slidingcomponents) of the slag separating apparatus 50 and serves as alubricant for those frictional components of the slag separatingapparatus 50. Therefore, the cleaning water is effective to reduce noiseand wear of the slag separating apparatus 50.

[0047] The method for cleaning water-quenched slag 122 in the slagseparating apparatus 50 is not limited to the method for supplying thecleaning water from the spraying nozzle 55. Any method capable ofcleaning the water-quenched slag 122 which has been conveyed out of theslag cooling water 152 in the water tank 51 may be used.

[0048] Even if a means for preventing the gas-liquid contact of theexhaust gas 112 and the slag cooling water 152 by blowing air (purgeair) or inert gas (purge inert gas) from the gas blowing line 131 to thedischarge end of the water quenching trough 30 is provided, the slagcooling water 152 is not fully effective to prevent the slag coolingwater 152 from being contaminated on long-term basis. However, as in theembodiment of FIG. 2, using the spraying nozzle 55 together with the gasblowing line 131 is effective to recover the water-quenched slag of goodquality.

[0049] Further, as shown in FIG. 2, the slag discharge chute 21 has asuction port 23 for drawing in a mixture of the air or inert gas 132introduced into the water quenching trough 30 and the exhaust gas 112.The suction port 23 is connected to a gas mixture line 141 which has adamper 24 for controlling the flow rate of the gas mixture drawn fromthe suction port 23 and a suction fan 22. The suction fan 22 has anoutlet connected to a gas mixture blowing line 142 for blowing the gasmixture into the tertiary combustion chamber 13 of the slaggingcombustion furnace 10.

[0050] Further, a temperature sensor 25 is provided in the gas mixtureline 141, and the output of the temperature sensor 25 is supplied to atemperature controller 26 which controls the opening of the damper 24and/or the rotational speed of a drive motor M of the suction fan 22 sothat a flow rate of the gas mixture is controlled to keep the gasmixture line 141 at a predetermined set temperature.

[0051] As described above, the temperature sensor 25 is provided in thegas mixture line 141 to control the circulating flow rate of the air orinert gas 132 and the exhaust gas 112 in order to keep the temperatureof the gas mixture line 141 at a set temperature. Thus, the temperatureof the gas mixture line 141 can be lowered to a allowable temperature ofthe suction fan 22. By keeping the gas mixture line 141 at a temperatureequal to or higher than the dew point of hydrogen chloride contained inthe exhaust gas, an occurrence of low-temperature corrosion of ductswhich define the gas mixture line 141 and the gas mixture blowing line142, and the suction fan 22 is prevented.

[0052] If a gas blown from the gas blowing line 131 is air, then the airis supplied as combustion air through the gas mixture blowing line 142to the tertiary combustion chamber 13 of the slagging combustion furnace10.

[0053] In the above embodiment, the temperature controller 26 controlsthe opening of the damper 24 and/or the rotational speed of the drivemotor M for driving the section fan 22 to control the rate of the gasmixture. However, the temperature controller 26 may be used to controlthe rate of the air or inert gas 132 introduced from the gas blowingline 131 or control the rate of the exhaust gas through the gas mixtureline 141 while keeping the rate of the air or inert gas 132 constant.That is, either the rate of the air or inert gas 132 introduced from thegas blowing line 131 or the rate of the exhaust gas 112 through the gasmixture line 141 may be controlled.

[0054] Further, in the slagging combustion furnace 10 shown in FIG. 2, atemperature sensor may be installed near the slag discharge port 14 ofthe slagging combustion furnace 10, and based on an output signal of thetemperature sensor, the temperature controller 26 may control theopening of the damper 24 and/or the rotational speed of the drive motorM for driving the suction fan 22 to control the rate of the gas mixtureof the air or inert gas 132 and the exhaust gas 112, thereby keeping thetemperature of the slag discharge port 14 at a set temperature.

[0055] In this manner, by providing the temperature sensor near the slagdischarge port 14 and controlling the flow rate of the gas mixture inorder to keep the temperature of the slag discharge port 14 and theportion around the slag discharge port 14 at a set temperature or tokeep the amount of slag attached to the slag discharge port 14 at apredetermined amount or less, based on an output signal from thetemperature sensor serving as a flow control means, the slag dischargeport 14 can have a desired level of dischargeability of molten slag. Forexample, by varying the rate of the gas mixture while keeping thetemperature of the mixture of the exhaust gas and the air or inert gasconstant, while heat resistance of the suction fan is ensured andlow-temperature corrosion of the suction fan is prevented fromoccurring, a desired level of dischargeability of molten slag can bemaintained.

[0056] When the slag discharge port is clogged for some reason, a burner170 is operated to produce flames 171 to melt away the slag attached tothe slag discharge port 14 and the portion around the slag dischargeport 14, as shown in FIG. 3. Because the amount of a high-temperaturegas produced is greater at this time than at a normal operation of theswirling-type slagging combustion furnace, only the air or inert gas 132that is introduced is not sufficient enough to keep the gas mixture at adesired temperature, and the gas mixture tends to increase itstemperature unduly. In order to solve this problem, there is provided acooling water injecting mechanism having cooling water nozzles 173 forinjecting cooling water 172 into the slag discharge chute 21. When themixture gas suffers an undue temperature increase, cooling water isinjected into the slag discharge chute 21 to lower the temperature ofthe gas mixture. In the case where the amount of a high-temperature gasproduced is greater at this time than at a normal operation, the air orinert gas 132 may be introduced in an increased amount to cool thehigh-temperature gas. However, the air or inert gas 132 introduced in anincreased amount would bring about an increase in the amount of the gasmixture, resulting in an uneconomical gas circulation system design.Furthermore, the air or inert gas 132 may be reduced in amount dependingon the scale of the furnace. The cooling water injecting mechanism whichis used at all times in combination with the swirling-type slaggingcombustion furnace 10 is effective to reduce the temperature of theexhaust gas 112 and allows the gasification and slagging combustionsystem to have a wider range of applications.

[0057] The slag discharge port 14 may be cooled by water cooling tubes(water cooling structure) for increasing the durability of refractorymaterial for defining the slag discharge port 14. The slag dischargeport 14 thus cooled may be prevented from suffering an undue temperaturerise. In view of the possibility of an undue temperature reduction ofmolten slag, the swirling-type slagging combustion furnace 10 shouldpreferably be combined with an in-furnace ITV (Industrial Television)system, i.e., a remote monitoring system for monitoring the state ofmolten slag. The in-furnace ITV system has an ITV which may be locatedat a position for monitoring the slag discharge port.

[0058]FIG. 4 is a view showing a melting system according to anotherembodiment of the present invention.

[0059] The melting system shown in FIG. 4 differs from the meltingsystem shown in FIG. 2 in that a heat exchanger 42 is provided in a slagcooling water circulation line 151, the slag cooling water 152 in thewater tank 51 is delivered to the heat exchanger 42 by a pump 41, and byintroducing cooling water 153 from the outside, heat exchange betweenthe cooling water 153 and the slag cooling water 152 is performed tocool the slag cooling water 152.

[0060] The cooling water 153 is introduced through a conduit having acontrol valve 43 which is controlled by a controller 45 that monitorsthe temperature of the slag cooling water 152 based on an output signalfrom a temperature sensor 44. The controller 45 controls the opening ofthe control valve 43 to control the rate of the cooling water 153 tokeep the slag cooling water 152 at a set temperature.

[0061] The temperature of the slag cooling water 152 is increased whenthe slag cooling water 152 is brought into contact with thehigh-temperature molten slag 121. As the temperature of the slag coolingwater 152 is increased, the amount of the slag cooling water 152 whichis evaporated is also increased, and hence a large amount ofreplenishing water is required.

[0062] The increase of the amount of the evaporated slag cooling water152 causes the temperature of the gas mixture in the slag dischargechute 21 to be lowered. In order to keep the gas mixture in the gasmixture line 141 constant, it is necessary to draw in a large amount ofexhaust gas 112. Consequently, the gas mixture line 141, the gas mixtureblowing line 142, and the suction fan 22 become large in size, resultingin an increase in the construction cost.

[0063] Further, the slag separating apparatus 50 also suffers atemperature increase, and this temperature increase is not desirablefrom the standpoint of safety and working environments.

[0064] According to the present invention, the heat exchanger 42 isprovided in the slag cooling water circulation line 151, and heatexchange between the slag cooling water 152 in the water tank 51 of theslag separating apparatus 50 and the cooling water 153 supplied from theoutside is performed to keep the slag cooling water 152 in the watertank 51 of the slag separating apparatus 50 in a set (or preset)temperature range for thereby suppressing evaporation of the slagcooling water 152.

[0065]FIG. 5 schematically shows a melting system according to anotherembodiment of the present invention.

[0066] In the embodiment shown in FIGS. 2 and 4, the molten slag 121discharged from the slag discharge port 14 is discharged through thewater quenching trough 30 into the slag separating apparatus 50.However, the water quenching trough 30 may not necessarily be required.For example, as shown in FIGS. 5 and 6, molten slag 121 discharged fromthe slag discharge port 14 is directly discharged into the slag coolingwater 152 in the slag separating apparatus 50. The air or inert gas 132blown from the gas blowing line 131 is introduced between the slagdischarge port 14 and the water surface of the slag cooling water 152.

[0067] In the above embodiments, the slagging combustion furnacecomprises a swirling-type slagging combustion furnace. However, thepresent invention is not limited to a swirling-type slagging combustionfurnace, but is applicable to a melting furnace apparatus having amelting furnace for melting ash into molten slag, such as a plasmamelting furnace, a surface melting furnace, or the like.

[0068] A gasifying apparatus in the gasification and slagging combustionsystem according to the present invention has a gasification furnace forgasifying combustibles such as wastes, although such gasificationfurnace is not shown. The gasification furnace may comprise any desiredgasification furnace such as an internal circulating fluidized-bedgasification furnace, an external circulating fluidized-bed gasificationfurnace, or a kiln furnace. In the fluidized-bed gasification furnace, afluidized medium such as sand, Olivin sand, or alumina is used, and afluidizing gas such as preheated air, air, oxygen-enriched air, or steamis introduced from an air diffuser plate or air diffuser pipes to form acirculating flow of the fluidized medium in a fluidized bed. Thecirculating flow of the fluidized medium may be oriented in anydirection and is expected to provide an effect to transfer heat in thefluidized bed and an effect to crush materials such as wastes to betreated. The direction of the circulating flow of the fluidized mediummay be designed depending on the position where incombustibles arewithdrawn from the furnace. Various materials including wastes aresupplied to the fluidized bed from the location above the fluidized bedin which the circulating flow of the fluidized medium is formed, andpyrolyzed and gasified in the fluidized bed. The gas, which accompaniesash and pulverized carbon, produced in the fluidized-bed gasificationfurnace is then introduced into the subsequent slagging combustionfurnace (melting furnace) of the gasification and slagging combustionsystem according to the present invention.

[0069] As described above, according to the present invention, thefollowing excellent effects can be obtained.

[0070] (1) The gas blowing means is provided to blow air or inert gasbetween the slag discharge port of the slagging combustion furnace andthe surface of the slag cooling water, thus preventing exhaust gas fromcontacting the slag cooling water. Therefore, the slag cooling water isprevented from being lowered in quality. The water-quenched slag isprevented from being lowered in quality due to a reduced quality of theslag cooling water, i.e., the water-quenched slag is prevented frombeing lowered in quality due to contamination of the slag cooling water.Further, the slag discharge port and the portion around the slagdischarge port is prevented from being cooled due to steam generated byevaporation of the slag cooling water.

[0071] (2) The gas mixture line (the gas mixture drawing/blowing line)is provided to draw a mixed gas from the slag discharge portion of theslagging combustion furnace and to blow the mixed gas into the slaggingcombustion furnace. The gas mixture line draws the air or inert gasblown to the slag discharge portion and also steam produced byevaporation of the slag cooling water, thus preventing the slagdischarge port and the portion around the slag discharge port from beingcooled. The gas mixture line also draws the exhaust gas having a hightemperature through the slag discharge port, thus keeping the slagdischarge port and the portion around the slag discharge port at a hightemperature with the high-temperature exhaust gas and keepingdischargeability of the slag. The air that has been blown in is suppliedthrough the gas mixture line into the slagging combustion furnace,particularly a tertiary combustion chamber of the slagging combustionfurnace, and can be utilized as combustion air.

[0072] (3) By providing the flow control means, the flow rate of the gasmixture drawn from the slag discharge portion can be controlled.

[0073] (4) By providing the temperature sensor in the gas mixture line,the flow control means controls the flow rate of the gas mixture so asto keep the temperature of the gas mixture line at the set temperatureon a basis of the output from the temperature sensor. If the settemperature is set to a value equal to or lower than the allowabletemperature of the fan provided in the gas mixture line, then thetemperature of the gas mixture line can be kept to be equal to or lowerthan the allowable temperature of the fan. If the gas mixture line isoperated at a temperature of the dew point of hydrogen chloridecontained in the exhaust gas or higher, low-temperature corrosion ofducts which define the gas mixture line and the suction fan connectedthereto is prevented.

[0074] (5) Harmful impurities such as heavy metals attached to thesurfaces of the water-quenched slag can be removed from thewater-quenched slag by the cleaning water supplied from the cleaningwater supply system, and hence the water-quenched slag of good qualitycan be recovered.

[0075] Furthermore, even if the exhaust gas discharged together with themolten slag from the slagging combustion furnace is not completelyprevented from contacting the slag cooling water, the same cleaningeffect can be obtained.

[0076] (6) When the air or inert gas is blown between the slag dischargeport of the slagging combustion furnace and the surface of the slagcooling water, the exhaust gas is prevented from contacting the slagcooling water, and hence the slag cooling water is prevented from beinglowered in quality. The water-quenched slag is thus prevented from beinglowered in quality due to a reduced quality of the slag cooling water.

[0077] (7) After the water-quenched slag is scraped and removed from thebottom of the water tank and is conveyed above the surface of the slagcooling water in the water tank, the water-quenched slag is cleaned bythe cleaning water sprayed from the cleaning water supply system.Consequently, harmful impurities such as heavy metals attached to thesurfaces of the water-quenched slag can be removed from thewater-quenched slag, and hence the water-quenched slag of good qualitycan be recovered.

[0078] (8) The gas blowing means is provided to blow the air or inertgas between the slag discharge port of the slagging combustion furnaceand the surface of the slag cooling water, thus preventing exhaust gasdischarged from the slagging combustion furnace through the slagdischarge port from contacting the slag cooling water. Therefore, thegasification and slagging combustion system can be constructed such thatthe slag cooling water is prevented from being lowered in quality. Thewater-quenched slag is also prevented from being lowered in quality dueto a reduced quality of the slag cooling water.

[0079] (9) After the water-quenched slag is scraped and removed from thebottom of the water tank and is conveyed above the surface of the slagcooling water, the cleaning water supplied from the cleaning watersupply system is sprayed over the water-quenched slag to remove harmfulimpurities such as heavy metals attached to the surfaces of thewater-quenched slag. Therefore, the gasification and slagging combustionsystem which can recover the water-quenched slag of good quality can beconstructed.

INDUSTRIAL APPLICABILITY

[0080] The present invention is applicable to a melting system forbringing molten slag discharged from an ash melting furnace into contactwith water to produce water-quenched slag and a method of operating suchmelting system, and a melting system attached to a gasification andslagging combustion system for combusting and treating various wastesincluding municipal wastes, refuse-derived fuel (RDF), plastic wastes,waste FRP, biomass wastes, automobile wastes, waste oil, and the like.

1. An ash melting system comprising: a slagging combustion furnace formelting ash into molten slag and discharging the molten slag from a slagdischarge port; a slag separating apparatus for bringing the molten slaginto contact with slag cooling water to produce water-quenched slag, andseparating the water-quenched slag from the slag cooling water; and agas blowing means for blowing air or inert gas between said slagdischarge port of said slagging combustion furnace and the surface ofsaid slag cooling water.
 2. A system according to claim 1, furthercomprising: a gas mixture line for drawing a gas mixture of exhaust gasdischarged from said slag discharge port of said slagging combustionfurnace and the air or inert gas blown from said gas blowing means andsupplying said gas mixture into said slagging combustion furnace.
 3. Asystem according to claim 2, further comprising: a flow control meansprovided in said gas mixture line for controlling the flow rate of saidgas mixture drawn by said gas mixture line.
 4. A system according toclaim 3, further comprising: a temperature sensor provided in said gasmixture line for measuring the temperature of said gas mixture in saidgas mixture line; wherein said flow control means is operated on a basisof an output of said temperature sensor to control the flow rate of saidgas mixture drawn by said gas mixture line to equalize the temperatureof said gas mixture line with a set temperature.
 5. An ash meltingsystem comprising: a slagging combustion furnace for melting ash intomolten slag and discharging the molten slag from a slag discharge port;a slag separating apparatus for bringing the molten slag into contactwith slag cooling water to produce water-quenched slag, and separatingthe water-quenched slag from the slag cooling water, said slagseparating apparatus having a slag separating means and having a watertank with a settling and separating function; and a slag cleaning meansfor supplying cleaning water supplied from a cleaning water supplysystem to the water-quenched slag to clean the water-quenched slag afterthe water-quenched slag is removed from a bottom of said water tank andis conveyed above the surface of the slag cooling water in said watertank.
 6. A method of operating an ash melting system for producingwater-quenched slag from molten slag discharged from a slaggingcombustion furnace, and then separating the water-quenched slag fromslag cooling water, the method comprising: blowing air or inert gasbetween a slag discharge port of said slagging combustion furnace andthe surface of the slag cooling water.
 7. A method of operating an ashmelting system having a slag separating apparatus for producingwater-quenched slag from molten slag discharged from a slaggingcombustion furnace, and then separating the water-quenched slag fromslag cooling water with said slag separating apparatus, said slagseparating apparatus having a water tank with a settling and separatingfunction, the method comprising: supplying cleaning water supplied froma cleaning water supply means to the water-quenched slag to clean thewater-quenched slag after the water-quenched slag is removed from abottom of said water tank and is conveyed above the surface of the slagcooling water in said water tank.
 8. A gasification and slaggingcombustion system comprising: a gasification furnace for gasifyingwastes to generate gasification products; a slagging combustion furnacefor combusting said gasification products to produce molten slag; and agas blowing means for blowing air or inert gas between a slag dischargeport of said slagging combustion furnace and the surface of slag coolingwater.
 9. A gasification and slagging combustion system comprising: agasification furnace for gasifying wastes to generate gasificationproducts; a slagging combustion furnace for combusting said gasificationproducts to produce molten slag; a slag separating apparatus forproducing water-quenched slag from the molten slag discharged from saidslagging combustion furnace, and separating the water-quenched slag fromslag cooling water, said slag separating apparatus having a slagseparating means and having a water tank with a settling and separatingfunction; and a slag cleaning means for supplying cleaning watersupplied from a cleaning water supply means to the water-quenched slagto clean the water-quenched slag after the water-quenched slag isremoved from a bottom of the water tank and is conveyed above thesurface of the slag cooling water in said water tank.